When a loader will not inject
Most of the time this is one of four things: your antivirus removed the loader, a Windows security feature is blocking the injection, the loader is out of date against the current game build, or it was not run as administrator. They look identical from the outside, so work through them in order.
First, work out which failure you have
Two very different problems produce the same experience of "it does not work", and fixing the wrong one wastes an evening.
If the loader disappears after download, will not start, or vanishes from its folder, that is your antivirus. Nothing is wrong with the loader; it has been quarantined.
If the loader starts, runs, and then nothing happens in game — no menu, no keybind response — that is an injection failure, and antivirus is probably not involved.
Everything below assumes you downloaded from your own dashboard. A loader from a mirror, a Discord DM or a YouTube description is a different problem, and it is usually the one where people lose their accounts.
Antivirus removing the loader
This is normal and expected. Antivirus engines classify by behaviour, and software that attaches to a running game to modify its memory looks exactly like malware to a heuristic scanner. It is the same detection logic; the engine cannot tell intent.
Add the loader's folder to your exclusions rather than turning protection off across the whole machine. In Windows Security that is Virus & threat protection, then Manage settings, then Add or remove exclusions, and add the folder you keep it in.
You may need to re-download afterwards, because the file that was already quarantined stays quarantined. Turn real-time protection back on when you finish playing, and never disable it to run something you did not get from your dashboard.
Windows security features blocking injection
If the loader runs but nothing attaches, the usual cause is a Windows protection feature doing exactly its job. Memory integrity, sometimes listed as Core Isolation, and the virtualisation-based security features around it are designed to stop one process writing into another.
These live in Windows Security under Device security, Core isolation details. If Memory integrity is on, injection into the game process is likely to fail regardless of which product you are running.
Be clear-eyed about this: those features exist for a reason, and turning them off lowers your machine's defences generally, not only for the thing you want to run. That is a real trade rather than a formality.
Related, and easy to miss: run the loader as administrator. Attaching to another process needs the privilege, and without it the loader will start, appear to work, and do nothing.
The loader being out of date
FiveM and GTA V both update, and an update can move the things a loader is looking for. When that happens the loader attaches to nothing, or attaches and crashes the game, and no amount of exclusions or privilege changes it.
Check the status board before assuming your machine is at fault. If a product is listed as Updating, that is what you are experiencing, and the fix is a new build rather than anything on your end.
The same applies after a FiveM patch: give it a little time, then re-download from your dashboard rather than reusing the copy you already have.
Things that are not the problem
A few pieces of advice circulate that will not help. Reinstalling GTA V rarely changes anything, because the loader is not attaching to a corrupted file, it is being blocked. Turning off your firewall does nothing, because this is not a network problem. Running in compatibility mode does nothing.
Reinstalling FiveM itself does occasionally help, but for a different reason than people think: it clears cached data that may be stale, which is the same reason it is a first step for token bans.
If you have worked through everything here and it still will not attach, that is worth a support ticket rather than more guessing. Include which product, which build, and which of the two failure types you have, because those three facts answer most of it immediately.
Common questions
Because it looks like malware to a heuristic scanner. Antivirus engines classify by behaviour, and software that attaches to a running game to modify its memory behaves exactly like something malicious. The engine cannot tell the difference in intent, so the flag is expected rather than a sign the file is broken.
Add the loader's folder to your exclusions instead, which is narrower than disabling protection across the whole machine. Re-enable real-time protection when you finish. Never disable protection to run something you did not download from your own dashboard, because that is the situation where the warning is likely to be real.
That is an injection failure rather than an antivirus problem. The three common causes are Windows memory integrity or virtualisation-based security blocking process access, the loader not being run as administrator, or the build being out of date against the current game version. Check the status board for the third before changing Windows settings.
Yes. Attaching to another running process requires the privilege, and without it the loader typically starts, looks like it is working, and then does nothing at all. It is the quickest thing to rule out.
It genuinely lowers your machine's defences, not just for the thing you want to run, so treat it as a real trade rather than a formality. Memory integrity exists to stop one process writing into another, which is also the reason it blocks injection. If you turn it off, understand what you are turning off.
Almost never. The loader is not failing because a game file is corrupted, it is failing because something is blocking it or because the build no longer matches the game. Reinstalling FiveM occasionally helps for a different reason: it clears cached data that may be stale.